Protective circuit for current regulator

ABSTRACT

Current regulator device comprises constant current transformer having lighting circuit in its secondary and an open circuit protective device with time delay means connected to the transformer primary. The time delay means includes an RC circuit for delaying turnoff of the regulator in the event of a break in the lighting circuit.

United States Patent Clair A. Nodurft East Flat Rock, NC. 81,411

Oct. 16, 1970 Dec. 7, 1971 General Electric Company lnventor Appl. No.Filed Patented Assignee PROTECTIVE CIRCUIT FOR CURRENT REGULATOR 8Claims, 1 Drawing Fig.

US. Cl 317/30, 7

I 3 17/36 TD, 323/6, 3l5/l93 lnt.Cl. ..l-l05b 37/02, GOln l9/l6 Field ofSearch 317/30, 36

References Cited UNITED STATES PATENTS 7/1951 Houser et al 317/30 3/1958l-lauck et al..... 323/6 9/l958 Swasey 315/193 lll969 Minks... 323/228/1970 Jones.... 323/6 Primary Examiner-L. T. Hix I Attorneys-SidneyGreenberg, J. Wesley Haubner, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. F orman ABSTRACT: Currentregulator device comprises constant current transformer having lightingcircuit in its secondary and an open circuit protective device with timedelay means connected to the transformer primary. The time delay meansincludes an RC circuit for delaying turnoff of the regulator in theevent of a break in the lighting circuit.

PROTECTIVE CIRCUIT FOR CURRENT REGULATOR The present invention relatestocurrent regulator devices, and more particularly to constant currentregulators such as use d,in lighting circuits for supplying selectedcurrent levels for desired lamp brightness.

Arnong'lighting circuits of the above type in which the invention may beadvantageously employed are those used for lighting airport runways andtaxiways.

It is an object of the invention to provide an open'circuit protectivedevice with improved time-delay means for a current regulator.

It is a further object of the invention to provide a current regulatorcircuit with an open circuit protector device of the above type which isreliable inoperation even under varying ambient conditions, isrelatively'low in cost, is readily-adjustable to provide the desire timedelay period and is simple and compact in fonn.

Still another object of the invention is to provide a protectivecircuitof the above type which is immediately reset for furtheroperation after being actuated.

Other objects and advantages will become apparent from thefollowing'description and the appended claims.

With the above objects in view, the present invention relates in one ofits aspects to a current regulator system comprising,

in combination, a transformer having a primary winding and a secondarywinding, a load'circuit connected to the secondary winding, .terminalmeans for-connecting'the primary winding to a source of alternatingcurrent, main switch means connected between the primary winding andtheterminal means, sensing means in the load circuit responsive to currentin the latter circuit, a protector circuit connected to the main switchmeans for controlling the operation thereof, means for supplyingcurrentto the protector circuit, the protector circuit comprising firstoperating means for operating the main switch means, RC time delay meansconnected to the current supply means and to the first operating meansfor actuating the latter following a predetermined interval afterenergization of the RC-time delay means, and second operating meansconnected to the RC time delay means and the sensing means andresponsive to the latter means for controlling the energizaa'on of theRC time delay means in response to current condition in the loadcircuit, whereby upon interruption of current in the load circuit whilethe transformer primary winding is energized, the RC time delay meansactuates the first operating means to open the main switch means afterthe predetermined intervalfor deenergizing the transformer primarywinding, whereas return of current to the load circuit before thepredetermined interval elapses renders the RC time delay rent regulatorcircuit with an open circuit protective system showing an embodiment ofthe present invention.

Referring now to the drawing, there is shown a constant current serieslighting system applicable for airport lighting purposes. The systemillustrated comprisesa load circuit 1 in which the load comprises aplurality of series connected lamps 2, which may be of incandescent,gaseous discharge or other type. Load circuit 1 is connected to thesecondary winding 3b of a constant current transformer '3, such as amovable coil type, having its primary winding 3a connected to terminals4 of a source of alternating current. Arranged in series in the supplyleads 5a, 5b to transformer primary 3a are normally open switch contacts6b, 6c of main switch 6 which controls the power to transformer 3, themain switch contacts being operated by relay coil 6a connected in theprotector circuit as sociated with the constant current circuit, asdescribed more fully below.

in circuits of the type described, it has been the practice to provideprotection against the high open circuit voltage which occurs in theload circuit in the event of a break therein for any reason while theinput circuit is still energized. ln known circuits of this type, delaymeans have been incorporated for preventing permanenttripping of theprotector circuit in the event of momentary interruption of current inthe-load circuit. Such momentary interruption may occur, for example; incertain circuits in the courseof changing the brightness levels of thelighting means, or as a result of flashing the light sources forsignalling purposes. Delay devices heretofore used in such circuits haveincluded mechanical devices suchasbimetallic thermal switches, butthesehave not been'fully satisfactory due to malfunctions resulting fromrapidlyrepeated operation giving rise to excessive heat in the device.Transistor or like electronic delay devices are in general too costlyfor general use in such protector circuits.

ln'accordance with the. present invention, a protector circuit with animproved time delay means'is provided which avoids the disadvantages ofthe known devices and reliably effects-thedesired time delay in theoperation of the open circuit protector device.

The protective system of the illustrated embodiment includes theprovision of a current transformer 7 connected in secondaryload'circuitl 'andhaving relay coil'9a of switch device 9 connected inits secondary as shown, along with series connected capacitor 8 which,by cancelling the inductance of relay coil 9a,'reduces the impedancepresented to current transformer 7.

The protector circuit provided by the invention comprises supply lines10a, lob'conne'cted to terminals -11 Ma source of alternating current,typically of 120 volts,"'-with a'switch 12, such as a manually operatedtype, connected in one of the supply lines; Connected acrossthe supplyis relay coil 6a which when energized operates to close the normallyopen contacts 6b, 6c of main switch 6. Also connected across the supplyin the protector circuit is an RC time delay network comprisingchargingcapacitor 13 connected at one side in series with fixed resistor14 and variable resistor 15. Resistor 14 serves to provide a minimumresistance in thisnetwork. Connected at the other side of capacitor 13is'current limiting resister 16 which-in turn is connected to the poleof single pole, double throw relay switch 9 which has a normally opencontact 9b and a normally closed contact 90. Contact 9b is connectedacross capacitor 13 and resistor 16 in series discharge relationtherewithyand contact is connected to supply line 10b, as shown.Connected across capacitor 13 is DC relay coil 17s of switch device 17which has a normally closed switch. I contact 17b arranged in supplyline 10a between'switch l2 and relay coil 6a in series therewith.

Diode 18 is connected to supply line 10a in series with vari-While'shown as a-manually operable switch, switch 12 may be operated bya photoelectric control device or may be a time switch for initiatingoperation of the lighting'circuit during hours of darkness or otherdesired period.

When switch '12 is closed, current will flow through normally closedcontact 17a thereby energizing relay coil 6a and closing contacts'6b,6c. Current also flows through the branch including normally closedcontact 90, resistor 16, capacitor 13,-resistors 14 and 15, and diode18, thereby beginning to charge capacitor 13. The adjustment of variableresistor 15 andthe magnitude of capacitor 13, as well as of the othercircuit components, are so chosen as to provide a desired period (e.g.,one second), for charging capacitor 13 to a voltage which is sufiicientto energize relay coil 17a for operating the latter.

While the foregoing operation is taking place, power is being appliedthrough closed switch 6 to constant current' the secondary of the lattertransformer. As a result, normally open contact 9b in the protectorcircuit closes and normally closed contact 90, opens before the onesecond period for charging capacitor 13 has elapsed. This conditionstops the charging of capacitor 13 and also results in dischargingcapacitor 13 instantaneously through resistor 16.

Normal operation of the lighting circuit thus continues until switch 12is opened or until the power supply to relay coil 60 is otherwiseinterrupted, resulting in opening of switch contacts 6b, 6c anddeenergizing the primary of transformer 3. Under these conditions, relayswitch 9 is also deenergized and its contacts 9b, 9c revert to theirnormal positions.

If during normal operation a break occurs in lighting circuit 1resulting in an open circuit while transformer 3 is still energized,relay switch 9 is deenergized with contact 9b opening and contact 90closing. Current now flows through resistors l4, l and 16 and diode 18to charge capacitor 13. After the charging period of about one' secondhas elapsed, the voltage on capacitor 13 is sufficient to energize relaycoil 17a, opening its normally closed contact 17b, and deenergizingrelay coil 60 so that its contacts 6b, 60 open and removed power fromtransformer 3.

In an illustrative circuit as described, the following components havetypical values as shown:

relistor 14 8,200 ohms resistor l5 H.000 ohml resistor 16 22 ohmscapacitor 13 33 microfarlds relay coil 17a l5,000 ohms pickup voltage-30 volts In a usual case, terminals 11 of the protector circuit areconnected to a relatively low voltage source, e.g., 120 volts AC, whileterminals 4 of the main current regulator circuit are connected to ahigher voltage source, e.g., 240 volts AC or higher. While separatepower sources are indicated in the circuit diagram for these respectivecircuits, it will be understood that the same power source may be usedfor both circuits, with a suitable transformer, for example, being usedto step up or step down the voltage as appropriate for the particularcircuit. While the present invention has been described with referenceto particular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended cover all such equivalent variations as come withinthe true spirit and scope of the invention.

What I claim as new and desire to secure to Letters Patent of the UnitedStates is:

1. Circuit protective system comprising, in combination, a source ofelectrical current, a load circuit connected to said source, switchmeans connected between said source and said load circuit forcontrolling supply of current to said load circuit, sensing means insaid load circuit responsive to current in the latter circuit, aprotector circuit connected to said switch means for controlling theoperation thereof, means for supplying current to said protectorcircuit, said protector circuit comprising first operating means foroperating said switch means, RC time delay means connected to saidcurrent supply means and to said first operating means for actuating thelatter following a predetermined interval after energization of said RCtime delay means, and second operating means connected to said RC timedelay means and said sensing means and responsive to the latter meansfor controlling the energization of said RC time delay means in responseto current condition renders said RC time delay means ineffective toopen said switch means. I

2. Current regulator system compnsing, In combination, a

transformer having a primary winding and a secondary winding a loadcircuit connected to said second winding, terminal means for connectingsaid primary winding to a source of alternating current, main switchmeans connected between said primary winding said terminal means,sensing means in said load circuit responsive to current in the lattercircuit, a protector circuit connected to said main switch means, forcontrolling the operation thereof, means for supplying current to saidprotector circuit, said protector circuit comprising first operatingmeans for operating said main switch means, RC time delay meansconnected to said current supply means and to said first operating meansfor actuating the latter following a predetermined interval afterenergization of said RC time delay means, and second operating meansconnected to said RC time delay means and said sensing means andresponsive to the latter means for controlling the energization of saidRC time delay means in response to current condition in said loadcircuit, whereby upon interruption of current in said load circuit whilesaid transformer primary winding is energized, said RC time delay meansactuates said first operating means to open said main switch means aftersaid predetermined interval for deenergizing said transformer primarywinding, whereas return of current to said load circuit before saidpredetermined interval elapses renders said RC time delay meansineffective to open said main switch means.

3. A system as defined in claim 2, said RC time delay means comprisingseries connected resistance means and a capacitor, said first operatingmeans comprising first relay switch means having a first relay coilconnected across said capacitor and first normally closed contact meansconnected to said current supply means for controlling supply of currenttherefrom, said main switch means comprising a second relay coilconnected to said first normally closed contact means and having secondnormally open contact means connected between said primary winding andsaid terminal means.

4. A system as defined in claim 3, said second operating meanscomprising a third relay coil connected to said sensing means and havingthird normally open contact means and fourth normally closed contactmeans, said third contact means being connected across said capacitor inseries discharge relation therewith, said fourth contact means beingconnected to said current supply means in series with said capacitor.

5. A system as defined in claim 2, including diode means connected tosaid current supply means in series with said RC time delay means.

6. A system as defined in claim 2, including operating switch meansconnected to said current supply means for controlling the power to saidprotector circuit.

7. A system as defined in claim 4, including a first resistor connectedto said capacitor and the junction between said third and fourth contactmeans.

8. A system as defined in claim 3, said resistance means comprising avariable resistor.

It I t l i

1. Circuit protective system comprising, in combination, a source ofelectrical current, a load circuit connected to said source, switchmeans connected between said source and said load circuit forcontrolling supply of current to said load circuit, sensing means insaid load circuit responsive to current in the latter circuit, aprotector circuit connected to said switch means for controlling theoperation thereof, means for supplying current to said protectorcircuit, said protector circuit comprising first operating means foroperating said switch means, RC time delay means connected to saidcurrent supply means and to said first operating means for actuating thelatter following a predetermined interval after energization of said RCtime delay means, and second operating means connected to said RC timedelay means and said sensing means and responsive to the latter meansfor controlling the energization of said RC time delay means in responseto current condition in said load circuit, whereby upon interruption ofcurrent in said load circuit while said switch means is closed, said RCtime delay means actuates said first operating means to open said switchmeans after said predetermined interval for removing power to said loadcircuit, whereas return of current to said load circuit before saidpredetermined interval elapses renders said RC time delay meansineffective to open said switch means.
 2. Current regulator systemcomprising, in combination, a transformer having a primary winding and asecondary winding, a load circuit connected to said secondary winding,terminal means for connecting said primary winding to a source ofalternating current, main switch means connected between said primarywinding and said terminal means, sensing means in said load circuitresponsive to current in the latter circuit, a protector circuitconnected to said main switch means, for controlling the operationthereof, means for supplying current to said protector circuit, saidprotector circuit comprising first operating means for operating saidmain switch means, RC time delay means connected to said current supplymeans and to said first operating means for actuating the latterfollowing a predetermined interval after energization of said RC timedelay means, and second operating means connected to said RC time delaymeans and said sensing means and responsive to the latter means forcontrolling the energization of said RC time delay means in response tocurrent condition in said load circuit, whereby upon interruption ofcurrent in said load circuit while said transformer primary winding isenergized, said RC time delay means actuates said first operating meansto open said main switch means after said predetermined interval fordeenergizing said transformer primary winding, whereas return of currentto said load circuit before said predetermined interval elapses renderssaid RC time delay means ineffective to open said main switch means. 3.A system as defined in claim 2, said RC time delay means comprisingseries connected resistance means and a capacitor, said first operatingmeans comprising first relay switch means having a first relay coilconnected across said capacitor and first normally closed contact meansconnected to said current supply means for controlling supply of currenttherefrom, said main switch means comprising a second relay coilconnected to said first normally closed contact means and having secondnormally open contact means connected between said primary winding andsaid terminal means.
 4. A system as defined in claim 3, said secondoperating means comprising a third relay coil connected to said sensingmeans and having third normally open contact means and fourth normallycloSed contact means, said third contact means being connected acrosssaid capacitor in series discharge relation therewith, said fourthcontact means being connected to said current supply means in serieswith said capacitor.
 5. A system as defined in claim 2, including diodemeans connected to said current supply means in series with said RC timedelay means.
 6. A system as defined in claim 2, including operatingswitch means connected to said current supply means for controlling thepower to said protector circuit.
 7. A system as defined in claim 4,including a first resistor connected to said capacitor and the junctionbetween said third and fourth contact means.
 8. A system as defined inclaim 3, said resistance means comprising a variable resistor.